<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        td{
            border: 1px solid red;
            background: #5CFF2E;
        }
    </style>
</head>
<body>
<script>
    document.write('<table>');
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        for (s=1;s<=a;s++){
            document.write('<td>'+s+'+'+a+'='+(a+s)+'</td>')
        }
        document.write('<br>');
        document.write('</tr>');
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    document.write('</table>');
</script>
</body>
</html>